There are known a mobile object monitoring system which monitors a mobile object (e.g., a portable terminal) by detecting the current position of the mobile object and a monitoring method for the system. For example, Japanese Patent Laid-Open No. 2002-281694 (reference 1) discloses a technique of causing a system center to transmit warning information and the current position information of a monitoring target terminal to a monitor terminal when an action area map does not coincide with the current position of the monitoring target terminal. In addition, this reference also discloses that when the distance between the monitoring target terminal and the monitor terminal becomes a predetermined value or more, warning information is transmitted.
Japanese Patent Laid-Open No. 2000-215374 (reference 2) discloses a technique in which when the distance between a terminal communication device attached to a baggage and a PHS (Personal Handyphone System) terminal carried by the owner becomes a predetermined value or more, the PHS terminal generates a warning or the like, and the terminal communication device notifies the PHS terminal of specific information via an existing mobile communication network.
In addition, Japanese Patent Laid-Open No. 2004-294377 (reference 3) discloses a technique of checking whether a portable terminal device can reach a specific position from the current position within a predetermined time, and generating a warning from a monitoring device to the portable terminal device when the portable terminal device exceeds the return limit distance.
Furthermore, Japanese Patent Laid-Open No. 2004-355243 (reference 4) discloses a technique of causing a monitoring target to transmit emergency transmission mail to a monitor and causing the monitor to transmit emergency response mail to the monitoring target.